This invention pertains to drill pipe used in rotary drilling of the earth and more particularly to such drill pipe incorporating a sleeve thereabout to protect the pipe against wear.
A description of the prior art of drill pipe protectors appears in the aforementioned U.S. Pat. No. 4,146,060.
The process of centrifugally casting metals such as steel and of such casting incorporating two different materials, i.e. dual metal centrifugal casting is known and is described for example in a publication constituting the general catalog of the Industrial Products Division of United States Pipe and Foundry Company, bearing the notation "10-75" on the back thereof, a copy of which accompanies this application.
The aforementioned catalog describes various applications of dual casting, for example, on pages 23-24 is described a roll shell having an exterior of "Alloy 250", which is a hard alloy steel, and an interior of ductile iron, the shell being shrink fitted to a mandrel to produce a roll. Other applications are described.